With the British number one looking to seal victory she stuttered allowing Martic to begin an impressive fightback.

BBC: Elena Baltacha, Melanie South & Katie O'Brien go out

She will play Kaia Kanepi of Estonia in the last eight with the other quarterfinal between Bojana Jovanovski and Petra Martic.

CNN: STORY HIGHLIGHTS

The women's 2011 winner Sam Stosur was drawn against Croatia's Petra Martic, with top seed Victoria Azarenka playing world No. 74 Alexandra Panova.

CNN: Tennis legends tip Murray for grand slam glory at U.S. Open